Presynaptic inhibition of diverse afferents to the locus ceruleus by kappa-opiate receptors: a novel mechanism for regulating the central norepinephrine system

Prolactin in sleep and EEG regulation: New mechanisms and sleep-related brain targets complement classical data

The role of prolactin in sleep regulation has been the subject of extensive research over the past 50 years, resulting in the identification of multiple, disparate functions for the hormone. Prolactin demonstrated a characteristic circadian release pattern with elevation during dark and diminution during light. High prolactin levels were linked to non-rapid eye movement sleep and electroencephalogram delta activity in humans. Conversely, hyperprolactinemia showed strong correlation with REM sleep in rodent studies. Prolactin may be implicated in the alterations in female sleep patterns observed during the reproductive cycle, it may play a role in the REM sleep enhancement following stress and in sleep-related immunological processes. In conclusion, prolactin appears to have a sleep-promoting role, particularly during the dark phase. However, it does not appear to play a central and coherent role in sleep regulation, as observed in some neuropeptides such as orexin. Conversely, its principal function may be to facilitate situational, yet adaptive, changes in sleep patterns in response to challenging physiological phases, such as those associated with stress, immunological challenges, or the reproductive cycle. Neuronal substrates for prolactin-mediated sleep effects remain unknown; however, recent rodent sleep studies may provide insights into the potential sites of these effects.

Opioid Mechanisms and the Treatment of Depression

Opioid receptors are widely expressed in the brain, and the opioid system has a key role in modulating mood, reward processing and stress responsivity. There is mounting evidence that the endogenous opioid system may be dysregulated in depression and that drug treatments targeting mu, delta and kappa opioid receptors may show antidepressant potential. The mechanisms underlying the therapeutic effects of opioid system engagement are complex and likely multi-factorial. This chapter explores various pathways through which the modulation of the opioid system may influence depression. These include impacts on monoaminergic systems, the regulation of stress and the hypothalamic-pituitary-adrenal axis, the immune system and inflammation, brain-derived neurotrophic factors, neurogenesis and neuroplasticity, social pain and social reward, as well as expectancy and placebo effects. A greater understanding of the diverse mechanisms through which opioid system modulation may improve depressive symptoms could ultimately aid in the development of safe and effective alternative treatments for individuals with difficult-to-treat depression.

Properties and modulation of excitatory inputs to the locus coeruleus

Excitatory inputs drive burst firing of locus coeruleus (LC) noradrenaline (NA) neurons in response to a variety of stimuli. Though a small number of glutamatergic LC afferents have been investigated, the overall landscape of these excitatory inputs is largely unknown. The current study used an optogenetic approach to isolate three glutamatergic afferents: the prefrontal cortex (PFC), lateral hypothalamus (LH) and periaqueductal grey (PAG). AAV5-DIO-ChR2 was injected into each region in male and female CaMKII-Cre mice and the properties of excitatory inputs on LC-NA cells were measured. Notably we found differences among these inputs. First, the pattern of axonal innervation differed between inputs such that LH afferents were concentrated in the posterior portion of the LC-NA somatic region while PFC afferents were denser in the medial dendritic region. Second, basal intrinsic properties varied for afferents, with LH inputs having the highest connectivity and the largest amplitude excitatory postsynaptic currents while PAG inputs had the lowest initial release probability. Third, while orexin and oxytocin had minimal effects on any input, dynorphin strongly inhibited excitatory inputs originating from the LH and PAG, and corticotrophin releasing factor (CRF) selectively inhibited inputs from the PAG. Overall, these results demonstrate that individual afferents to the LC have differing properties, which may contribute to the modularity of the LC and its ability to mediate various behavioural outcomes. KEY POINTS: Excitatory inputs to the locus coeruleus (LC) are important for driving noradrenaline neuron activity and downstream behaviours in response to salient stimuli, but little is known about the functional properties of different glutamate inputs that innervate these neurons We used a virus-mediated optogenetic approach to compare glutamate afferents from the prefrontal cortex (PFC), the lateral hypothalamus (LH) and the periaqueductal grey (PAG). While PFC was predicted to make synaptic inputs, we found that the LH and PAG also drove robust excitatory events in LC noradrenaline neurons. The strength, kinetics, and short-term plasticity of each input differed as did the extent of neuromodulation by both dynorphin and corticotrophin releasing factor. Thus each input displayed a unique set of basal properties and modulation by peptides. This characterization is an important step in deciphering the heterogeneity of the LC.

Addiction and the cerebellum with a focus on actions of opioid receptors

Increasing evidence suggests that the cerebellum could play a role in the higher cognitive processes involved in addiction as the cerebellum contains anatomical and functional pathways to circuitry controlling motivation and saliency. In addition, the cerebellum exhibits a widespread presence of receptors, including opioid receptors which are known to play a prominent role in synaptic and circuit mechanisms of plasticity associated with drug use and development of addiction to opioids and other drugs of abuse. Further, the presence of perineural nets (PNNs) in the cerebellum which contain proteins known to alter synaptic plasticity could contribute to addiction. The role the cerebellum plays in processes of addiction is likely complex, and could depend on the particular drug of abuse, the pattern of use, and the stage of the user within the addiction cycle. In this review, we discuss functional and structural modifications shown to be produced in the cerebellum by opioids that exhibit dependency-inducing properties which provide support for the conclusion that the cerebellum plays a role in addiction.

Why It Is Important to Consider the Effects of Analgesics on Sleep: A Critical Review

We review the known physiological mechanisms underpinning all of pain processing, sleep regulation, and pharmacology of analgesics prescribed for chronic pain. In particular, we describe how commonly prescribed analgesics act in sleep-wake neural pathways, with potential unintended impact on sleep and/or wake function. Sleep disruption, whether pain- or drug-induced, negatively impacts quality of life, mental and physical health. In the context of chronic pain, poor sleep quality heightens pain sensitivity and may affect analgesic function, potentially resulting in further analgesic need. Clinicians already have to consider factors including efficacy, abuse potential, and likely side effects when making analgesic prescribing choices. We propose that analgesic-related sleep disruption should also be considered. The neurochemical mechanisms underlying the reciprocal relationship between pain and sleep are poorly understood, and studies investigating sleep in those with specific chronic pain conditions (including those with comorbidities) are lacking. We emphasize the importance of further work to clarify the effects (intended and unintended) of each analgesic class to inform personalized treatment decisions in patients with chronic pain. © 2021 American Physiological Society. Compr Physiol 11:1-31, 2021.

Consideration of sex as a biological variable in the translation of pharmacotherapy for stress-associated drug seeking

Stress is a frequent precipitant of relapse to drug use. Pharmacotherapies targeting a diverse array of neural systems have been assayed for efficacy in attenuating stress-induced drug-seeking in both rodents and in humans, but none have shown enough evidence of utility to warrant routine use in the clinic. We posit that a critical barrier in effective translation is inattention to sex as a biological variable at all phases of the research process. In this review, we detail the neurobiological systems implicated in stress-induced relapse to cocaine, opioids, methamphetamine, and cannabis, as well as the pharmacotherapies that have been used to target these systems in rodent models, the human laboratory, and in clinical trials. In each of these areas we additionally describe the potential influences of biological sex on outcomes, and how inattention to fundamental sex differences can lead to biases during drug development that contribute to the limited success of large clinical trials. Based on these observations, we determine that of the pharmacotherapies discussed only α₂-adrenergic receptor agonists and oxytocin have a body of research with sufficient consideration of biological sex to warrant further clinical evaluation. Pharmacotherapies that target β-adrenergic receptors, other neuroactive peptides, the hypothalamic-pituitary-adrenal axis, neuroactive steroids, and the endogenous opioid and cannabinoid systems require further assessment in females at the preclinical and human laboratory levels before progression to clinical trials can be recommended.

Depletion of the Microbiome Alters the Recruitment of Neuronal Ensembles of Oxycodone Intoxication and Withdrawal

Substance use disorders have a complex etiology. Genetics, the environment, and behavior all play a role in the initiation, escalation, and relapse of drug use. Recently, opioid use disorder has become a national health crisis. One aspect of opioid addiction that has yet to be fully examined is the effects of alterations of the microbiome and gut-brain axis signaling on central nervous system activity during opioid intoxication and withdrawal. The effect of microbiome depletion on the activation of neuronal ensembles was measured by detecting Fos-positive (Fos+) neuron activation during intoxication and withdrawal using a rat model of oxycodone dependence. Daily oxycodone administration (2 mg/kg) increased pain thresholds and increased Fos+ neurons in the basolateral amygdala (BLA) during intoxication, with a decrease in pain thresholds and increase in Fos+ neurons in the periaqueductal gray (PAG), central nucleus of the amygdala (CeA), locus coeruleus (LC), paraventricular nucleus of the thalamus (PVT), agranular insular cortex (AI), bed nucleus of the stria terminalis (BNST), and lateral habenula medial parvocellular region during withdrawal. Microbiome depletion produced widespread but region- and state-specific changes in neuronal ensemble activation. Oxycodone intoxication and withdrawal also increased functional connectivity among brain regions. Microbiome depletion resulted in a decorrelation of this functional network. These data indicate that microbiome depletion by antibiotics produces widespread changes in the recruitment of neuronal ensembles that are activated by oxycodone intoxication and withdrawal, suggesting that the gut microbiome may play a role in opioid use and dependence. Future studies are needed to better understand the molecular, neurobiological, and behavioral effects of microbiome depletion on addiction-like behaviors.

The role of catecholamines in modulating responses to stress: Sex-specific patterns, implications, and therapeutic potential for post-traumatic stress disorder and opiate withdrawal

Emotional arousal is one of several factors that determine the strength of a memory and how efficiently it may be retrieved. The systems at play are multifaceted; on one hand, the dopaminergic mesocorticolimbic system evaluates the rewarding or reinforcing potential of a stimulus, while on the other, the noradrenergic stress response system evaluates the risk of threat, commanding attention, and engaging emotional and physical behavioral responses. Sex-specific patterns in the anatomy and function of the arousal system suggest that sexually divergent therapeutic approaches may be advantageous for neurological disorders involving arousal, learning, and memory. From the lens of the triple network model of psychopathology, we argue that post-traumatic stress disorder and opiate substance use disorder arise from maladaptive learning responses that are perpetuated by hyperarousal of the salience network. We present evidence that catecholamine-modulated learning and stress-responsive circuitry exerts substantial influence over the salience network and its dysfunction in stress-related psychiatric disorders, and between the sexes. We discuss the therapeutic potential of targeting the endogenous cannabinoid system; a ubiquitous neuromodulator that influences learning, memory, and responsivity to stress by influencing catecholamine, excitatory, and inhibitory synaptic transmission. Relevant preclinical data in male and female rodents are integrated with clinical data in men and women in an effort to understand how ideal treatment modalities between the sexes may be different.

Opioid receptors mRNAs expression and opioids agonist-dependent G-protein activation in the rat brain following neuropathy

Potent opioid-based therapies are often unsuccessful in promoting satisfactory analgesia in neuropathic pain. Moreover, the side effects associated with opioid therapy are still manifested in neuropathy-like diseases, including tolerance, abuse, addiction and hyperalgesia, although the mechanisms underlying these effects remain unclear. Studies in the spinal cord and periphery indicate that neuropathy alters the expression of mu-[MOP], delta-[DOP] or kappa-[KOP] opioid receptors, interfering with their activity. However, there is no consensus as to the supraspinal opioidergic modulation provoked by neuropathy, the structures where the sensory and affective-related pain components are processed. In this study we explored the effect of chronic constriction of the sciatic nerve (CCI) over 7 and 30 days (CCI-7d and CCI-30d, respectively) on MOP, DOP and KOP mRNAs expression, using in situ hybridization, and the efficacy of G-protein stimulation by DAMGO, DPDPE and U-69593 (MOP, DOP and KOP specific agonists, respectively), using [35S]GTPγS binding, within opioid-sensitive brain structures. After CCI-7d, CCI-30d or both, opioid receptor mRNAs expression was altered throughout the brain: MOP - in the paracentral/centrolateral thalamic nuclei, ventral posteromedial thalamic nuclei, superior olivary complex, parabrachial nucleus [PB] and posterodorsal tegmental nucleus; DOP - in the somatosensory cortex [SSC], ventral tegmental area, caudate putamen [CPu], nucleus accumbens [NAcc], raphe magnus [RMg] and PB; and KOP - in the locus coeruleus. Agonist-stimulated [35S]GTPγS binding was altered following CCI: MOP - CPu and RMg; DOP - prefrontal cortex [PFC], SSC, RMg and NAcc; and KOP - PFC and SSC. Thus, this study shows that several opioidergic circuits in the brain are recruited and modified following neuropathy.

The alpha- and beta-noradrenergic receptors blockade in the dorsal raphe nucleus impairs the panic-like response elaborated by medial hypothalamus neurons

Dorsal raphe nucleus (DRN) neurons are reciprocally connected to the locus coeruleus (LC) and send neural pathways to the medial hypothalamus (MH). The aim of this work was to investigate whether the blockade of α₁-, α₂- or β-noradrenergic receptors in the DRN or the inactivation of noradrenergic neurons in the LC modify defensive behaviours organised by MH neurons. For this purpose, Wistar male rats received microinjections of WB4101, RX821002, propranolol (α₁-_, α₂- and β-noradrenergic receptor antagonists, respectively) or physiological saline in the DRN, followed 10 min later by MH GABA_A receptor blockade. Other groups of animals received DSP-4 (a noradrenergic neurotoxin), physiological saline or only a needle insertion (sham group) into the LC, and 5 days later, bicuculline or physiological saline was administered in the MH. In all these cases, after MH treatment, the frequency and duration of defensive responses were recorded over 15 min. An anterograde neural tract tracer was also deposited in the DRN. DRN neurons send pathways to lateral and dorsomedial hypothalamus. Blockade of α₁- and β-noradrenergic receptors in the DRN decreased escape reactions elicited by bicuculline microinjections in the MH. In addition, a significant increase in anxiety-like behaviours was observed after the blockade of α₂-noradrenergic receptors in the DRN. LC pretreatment with DSP-4 decreased both anxiety- and panic attack-like behaviours evoked by GABA_A receptor blockade in the MH. In summary, the present findings suggest that the norepinephrine-mediated system modulates defensive reactions organised by MH neurons at least in part via noradrenergic receptors recruitment on DRN neurons.

Reduced Sensory-Evoked Locus Coeruleus-Norepinephrine Neural Activity in Female Rats With a History of Dietary-Induced Binge Eating

Noradrenergic pathways have been implicated in eating pathologies. These experiments sought to examine how dietary-induced binge eating influences the neuronal activity of the locus coeruleus (LC)-norepinephrine (NE) system. Young adult female Sprague Dawley rats (7-8 weeks old) were exposed to a repeated intermittent (twice weekly) cycle of 30-min access to a highly palatable sweetened fat (i.e., vegetable shortening with 10% sucrose) with or without intermittent (24 h) calorie restriction (Restrict Binge or Binge groups, respectively). Age- and weight-matched female control rats were exposed to standard chow feeding (Naive group) or intermittent chow feeding (Restrict group). The Binge and Restrict Binge groups demonstrated an escalation in sweet-fat food intake after 2.5 weeks. On week 3, in vivo single-unit LC electrophysiological activity was recorded under isoflurane anesthesia. Restrict Binge (20 cells from six rats) and Binge (27 cells from six rats) had significantly reduced (approximate 20% and 26%, respectively) evoked LC discharge rates compared with naive rats (22 cells, seven rats). Spontaneous and tonic discharge rates were not different among the groups. Signal-to-noise ratio was reduced in the groups with intermittent sweetened fat exposure. In order to investigate the neuropeptide alterations as a consequence of dietary binge eating, relative gene expression of neuropeptide Y (NPY), glucagon-like peptide 1 receptor (GLP-1r), prodynorphin, and related genes were measured in LC and hypothalamic arcuate (Arc) regions. Glp-1r, Npy2r, and Pdyn in LC region were reduced with repeated intermittent restriction. Npy1r was reduced by approximately 27% in ARC of Restrict compared with Naive group. Such data indicate that dietary-induced binge eating alters the neural response of LC neurons to sensory stimuli and dampens the neural stress response.

The role of co-neurotransmitters in sleep and wake regulation

Sleep and wakefulness control in the mammalian brain requires the coordination of various discrete interconnected neurons. According to the most conventional sleep model, wake-promoting neurons (WPNs) and sleep-promoting neurons (SPNs) compete for network dominance, creating a systematic "switch" that results in either the sleep or awake state. WPNs and SPNs are ubiquitous in the brainstem and diencephalon, areas that together contain <1% of the neurons in the human brain. Interestingly, many of these WPNs and SPNs co-express and co-release various types of the neurotransmitters that often have opposing modulatory effects on the network. Co-transmission is often beneficial to structures with limited numbers of neurons because it provides increasing computational capability and flexibility. Moreover, co-transmission allows subcortical structures to bi-directionally control postsynaptic neurons, thus helping to orchestrate several complex physiological functions such as sleep. Here, we present an in-depth review of co-transmission in hypothalamic WPNs and SPNs and discuss its functional significance in the sleep-wake network.

The Paraventricular Hypothalamus Regulates Satiety and Prevents Obesity via Two Genetically Distinct Circuits

SIM1-expressing paraventricular hypothalamus (PVH) neurons are key regulators of energy balance. Within the PVH^SIM1 population, melanocortin-4 receptor-expressing (PVH^MC4R) neurons are known to regulate satiety and bodyweight, yet they account for only half of PVH^SIM1 neuron-mediated regulation. Here we report that PVH prodynorphin-expressing (PVH^PDYN) neurons, which notably lack MC4Rs, function independently and additively with PVH^MC4R neurons to account for the totality of PVH^SIM1 neuron-mediated satiety. Moreover, PVH^PDYN neurons are necessary for prevention of obesity in an independent but equipotent manner to PVH^MC4R neurons. While PVH^PDYN and PVH^MC4R neurons both project to the parabrachial complex (PB), they synaptically engage distinct efferent nodes, the pre-locus coeruleus (pLC), and central lateral parabrachial nucleus (cLPBN), respectively. PB-projecting PVH^PDYN neurons, like PVH^MC4R neurons, receive input from interoceptive ARC^AgRP neurons, respond to caloric state, and are sufficient and necessary to control food intake. This expands the CNS satiety circuitry to include two non-overlapping PVH to hindbrain circuits.

Active control of arousal by a locus coeruleus GABAergic circuit

Arousal responses linked to locus coeruleus noradrenergic (LC-NA) activity affect cognition. However, the mechanisms that control modes of LC-NA activity remain unknown. Here, we reveal a local population of GABAergic neurons (LC-GABA) capable of modulating LC-NA activity and arousal. Retrograde tracing shows that inputs to LC-GABA and LC-NA neurons arise from similar regions, though a few regions provide differential inputs to one subtype over the other. Recordings in the locus coeruleus demonstrate two modes of LC-GABA responses whereby spiking is either correlated or broadly anticorrelated with LC-NA responses, reflecting anatomically similar and functionally coincident inputs, or differential and non-coincident inputs, to LC-NA and LC-GABA neurons. Coincident inputs control the gain of LC-NA-mediated arousal responses, whereas non-coincident inputs, such as from the prefrontal cortex to the locus coeruleus, alter global arousal levels. These findings demonstrate distinct modes by which an inhibitory locus coeruleus circuit regulates arousal in the brain.

Untangling the complexity of opioid receptor function

Mu opioid receptor agonists are among the most powerful analgesic medications but also among the most addictive. The current opioid crisis has energized a quest to develop opioid analgesics that are devoid of untoward effects. Since their discovery in the 1970's, there have been major advances in our understanding of the endogenous opioid systems that these drugs target. Yet many questions remain and the development of non-addictive opioid analgesics has not been achieved. However, access to new molecular, genetic and computational tools have begun to elucidate the structural dynamics of opioid receptors, the scaffolding that links them to intracellular signaling cascades, their cellular trafficking and the distinct ways that various opioid drugs modify them. This mini-review highlights some of the chemical and pharmacological findings and new perspectives that have arisen from studies using these tools. They reveal multiple layers of complexity of opioid receptor function, including a spatiotemporal specificity in opioid receptor-induced cellular signaling, ligand-directed biased signaling, allosteric modulation of ligand interactions, heterodimerization of different opioid receptors, and the existence of slice variants with different ligand specificity. By untangling these layers, basic research into the chemistry and pharmacology of opioid receptors is guiding the way towards deciphering the mysteries of tolerance and physical dependence that have plagued the field and is providing a platform for the development of more effective and safer opioids.

Sex differences in morphine-induced trafficking of mu-opioid and corticotropin-releasing factor receptors in locus coeruleus neurons

The locus coeruleus (LC)-norepinephrine (NE) system is a key nucleus in which endogenous opioid and stress systems intersect to regulate the stress response. LC neurons of male rats become sensitized to stress following chronic morphine administration. Whether sex dictates this pattern of opioid-induced plasticity has not been demonstrated. Delineating the neurobiological adaptations produced by chronic opioids will enhance our understanding of stress vulnerability in opioid-dependent individuals, and may reveal how stress negatively impacts addiction recovery. In the present study, the effect of chronic morphine on the subcellular distribution of mu-opioid (MOR) and CRF receptors (CRFR) was investigated in the LC of male and female rats using immunoelectron microscopy. Results showed that placebo-treated females exhibited higher MOR and CRFR cytoplasmic distribution ratio when compared to placebo-treated males. Chronic morphine exposure induced a shift in the distribution of MOR immunogold-silver particles from the plasma membrane to the cytoplasm selectively in male LC neurons. Interestingly, chronic morphine exposure induced CRFR recruitment to the plasma membrane of both male and female LC neurons. These findings provide a potential mechanism by which chronic opioid administration increases stress vulnerability in males and females via an increase in surface availability of CRFR in LC neurons. However, our results also support the notion that cellular adaptations to chronic opioids differ across the sexes as redistribution of MOR following morphine exposure was only observed in male LC neurons.

Anti-stress neuropharmacological mechanisms and targets for addiction treatment: A translational framework

Stress-related substance use is a major challenge for treating substance use disorders. This selective review focuses on emerging pharmacotherapies with potential for reducing stress-potentiated seeking and consumption of nicotine, alcohol, marijuana, cocaine, and opioids (i.e., key phenotypes for the most commonly abused substances). I evaluate neuropharmacological mechanisms in experimental models of drug-maintenance and relapse, which translate more readily to individuals presenting for treatment (who have initiated and progressed). An affective/motivational systems model (three dimensions: valence, arousal, control) is mapped onto a systems biology of addiction approach for addressing this problem. Based on quality of evidence to date, promising first-tier neurochemical receptor targets include: noradrenergic (α1 and β antagonist, α2 agonist), kappa-opioid antagonist, nociceptin antagonist, orexin-1 antagonist, and endocannabinoid modulation (e.g., cannabidiol, FAAH inhibition); second-tier candidates may include corticotropin releasing factor-1 antagonists, serotonergic agents (e.g., 5-HT reuptake inhibitors, 5-HT3 antagonists), glutamatergic agents (e.g., mGluR2/3 agonist/positive allosteric modulator, mGluR5 antagonist/negative allosteric modulator), GABA-promoters (e.g., pregabalin, tiagabine), vasopressin 1b antagonist, NK-1 antagonist, and PPAR-γ agonist (e.g., pioglitazone). To address affective/motivational mechanisms of stress-related substance use, it may be advisable to combine agents with actions at complementary targets for greater efficacy but systematic studies are lacking except for interactions with the noradrenergic system. I note clinically-relevant factors that could mediate/moderate the efficacy of anti-stress therapeutics and identify research gaps that should be pursued. Finally, progress in developing anti-stress medications will depend on use of reliable CNS biomarkers to validate exposure-response relationships.

Kappa opioid receptor binding in major depression: A pilot study

Endogenous kappa opioids mediate pathological responses to stress in animal models. However, the relationship of the kappa opioid receptor (KOR) to life stress and to psychopathology in humans is not well described. This pilot study sought, for the first time, to quantify KOR in major depressive disorder (MDD) in vivo in humans using positron emission tomography (PET). KOR binding was quantified in vivo by PET imaging with the [11 C]GR103545 radiotracer in 13 healthy volunteers and 10 participants with current MDD. We examined the relationship between regional [11 C]GR103545 total volume of distribution (VT ) and diagnosis, childhood trauma, recent life stress, and, in a subsample, salivary cortisol levels during a modified Trier Social Stress Test (mTSST), amygdala, hippocampus, ventral striatum and raphe nuclei. Whole-brain voxel-wise analyses were also performed. [11 C]GR103545 VT did not differ significantly between MDD participants and healthy volunteers in the four a priori ROIs (p = 0.50). [11 C]GR103545 VT was unrelated to reported childhood adversity (p = 0.17) or recent life stress (p = 0.56). A trend-level inverse correlation was observed between [11 C]GR103545 VT and cortisol area-under-the curve with respect to ground during the mTSST (p = 0.081). No whole-brain voxel-wise contrasts were significant. Regional [11 C]GR103545 VT , a measure of in vivo KOR binding, does not differentiate MDD from healthy volunteers in this pilot sample. Future studies may examine KOR binding in subgroups of depressed individuals at increased risk for KOR abnormalities, including co-occurring mood and substance use disorders, as well as depression with psychotic features.

Persistent Stress-Induced Neuroplastic Changes in the Locus Coeruleus/Norepinephrine System

Neural plasticity plays a critical role in mediating short- and long-term brain responses to environmental stimuli. A major effector of plasticity throughout many regions of the brain is stress. Activation of the locus coeruleus (LC) is a critical step in mediating the neuroendocrine and behavioral limbs of the stress response. During stressor exposure, activation of the hypothalamic-pituitary-adrenal axis promotes release of corticotropin-releasing factor in LC, where its signaling promotes a number of physiological and cellular changes. While the acute effects of stress on LC physiology have been described, its long-term effects are less clear. This review will describe how stress changes LC neuronal physiology, function, and morphology from a genetic, cellular, and neuronal circuitry/transmission perspective. Specifically, we describe morphological changes of LC neurons in response to stressful stimuli and signal transduction pathways underlying them. Also, we will review changes in excitatory glutamatergic synaptic transmission in LC neurons and possible stress-induced modifications of AMPA receptors. This review will also address stress-related behavioral adaptations and specific noradrenergic receptors responsible for them. Finally, we summarize the results of several human studies which suggest a link between stress, altered LC function, and pathogenesis of posttraumatic stress disorder.

Contribution of Dynorphin and Orexin Neuropeptide Systems to the Motivational Effects of Alcohol

Understanding the neural systems that drive alcohol motivation and are disrupted in alcohol use disorders is of critical importance in developing novel treatments. The dynorphin and orexin/hypocretin neuropeptide systems are particularly relevant with respect to alcohol use and misuse. Both systems are strongly associated with alcohol-seeking behaviors, particularly in cases of high levels of alcohol use as seen in dependence. Furthermore, both systems also play a role in stress and anxiety, indicating that disruption of these systems may underlie long-term homeostatic dysregulation seen in alcohol use disorders. These systems are also closely interrelated with one another - dynorphin/kappa opioid receptors and orexin/hypocretin receptors are found in similar regions and hypocretin/orexin neurons also express dynorphin - suggesting that these two systems may work together in the regulation of alcohol seeking and may be mutually disrupted in alcohol use disorders. This chapter reviews studies demonstrating a role for each of these systems in motivated behavior, with a focus on their roles in regulating alcohol-seeking and self-administration behaviors. Consideration is also given to evidence indicating that these neuropeptide systems may be viable targets for the development of potential treatments for alcohol use disorders.

Co-localization of the cannabinoid type 1 receptor with corticotropin-releasing factor-containing afferents in the noradrenergic nucleus locus coeruleus: implications for the cognitive limb of the stress response

The noradrenergic system has been shown to play a key role in the regulation of stress responses, arousal, mood, and emotional states. Corticotropin-releasing factor (CRF) is a primary mediator of stress-induced activation of noradrenergic neurons in the nucleus locus coeruleus (LC). The endocannabinoid (eCB) system also plays a key role in modulating stress responses, acting as an "anti-stress" neuro-mediator. In the present study, we investigated the cellular sites for interactions between the cannabinoid receptor type 1 (CB1r) and CRF in the LC. Immunofluorescence and high-resolution immunoelectron microscopy showed co-localization of CB1r and CRF in both the core and peri-LC areas. Semi-quantitative analysis revealed that 44% (208/468) of CRF-containing axon terminals in the core and 35% (104/294) in the peri-LC expressed CB1r, while 18% (85/468) of CRF-containing axon terminals in the core and 6.5% (19/294) in the peri-LC were presynaptic to CB1r-containing dendrites. In the LC core, CB1r + CRF axon terminals were more frequently of the symmetric (inhibitory) type; while in the peri-LC, a majority were of the asymmetric (excitatory) type. Triple label immunofluorescence results supported the ultrastructural analysis indicating that CB1r + CRF axon terminals contained either gamma amino butyric acid or glutamate. Finally, anterograde transport from the central nucleus of the amygdala revealed that CRF-amygdalar afferents projecting to the LC contain CB1r. Taken together, these results indicate that the eCB system is poised to directly modulate stress-integrative heterogeneous CRF afferents in the LC, some of which arise from limbic sources.

The Role of NFkB in Drug Addiction: Beyond Inflammation

Aims

Nuclear factor kappa light chain enhancer of activated B cells (NFkB) is a ubiquitous transcription factor well known for its role in the innate immune response. As such, NFkB is a transcriptional activator of inflammatory mediators such as cytokines. It has recently been demonstrated that alcohol and other drugs of abuse can induce NFkB activity and cytokine expression in the brain. A number of reviews have been published highlighting this effect of alcohol, and have linked increased NFkB function to neuroimmune-stimulated toxicity. However, in this review we focus on the potentially non-immune functions of NFkB as possible links between NFkB and addiction.

Methods

An extensive review of the literature via Pubmed searches was used to assess the current state of the field.

Results

NFkB can induce the expression of a diverse set of gene targets besides inflammatory mediators, some of which are involved in addictive processes, such as opioid receptors and neuropeptides. NFkB mediates complex behaviors including learning and memory, stress responses, anhedonia and drug reward, processes that may lie outside the role of NFkB in the classic neuroimmune response.

Conclusions

Future studies should focus on these non-immune functions of NFkB signaling and their association with addiction-related processes.

Expression of protein kinase A and the kappa opioid receptor in selected brain regions and conditioned place aversion in morphine-dependent rats

This study examined adaptive changes in protein kinase A (PKA) and kappa opioid receptor (KOR) in selected addiction-related brain regions before and after conditioned place aversion (CPA). Seventy-two male SD rats were randomly assigned to an experimental group (morphine + naloxone, “MN”) and 2 control groups: MS (morphine + saline) and SN (saline + naloxone). MN rats were intraperitoneally injected with morphine twice per day for 6.5 days and naloxone once and trained to establish CPA model. MS and SN rats were injected with equivalent volumes of morphine plus saline and saline plus naloxone, respectively. PKA and KOR in AcbSH, CeA and VTA were measured by immunohistochemistry. Before CPA, there were no significant differences in PKA and KOR expression levels in the AcbSH, CeA and VTA between MN and 2 control groups. After CPA, significant differences in PKA expression were detected in the AcbSH (P<0.001) and VTA (P=0.018) between MN and 2 control groups. The average gray intensity of MN group (109.50±4.66) in AcbSH was significantly higher than that of MS (126.50±3.70, P<0.001) and MN (133.50±6.364, P<0.001) groups. Significant differences in KOR expression were also detected between MN and 2 control groups in CeA (P<0.001). In MN group, PKA and KOR expression levels showed adaptive changes at different points of CPA. These findings demonstrated that neuroadaptation mediated by PKA and KOR may be an important molecular neurobiology basis for CPA. The upregulation of AC-cAMP-PKA-CREB signaling pathway in AcbSH and VTA has some role in the neurobiological mechanism of CPA.

Role of the Dynorphin/Kappa Opioid Receptor System in the Motivational Effects of Ethanol

Evidence has demonstrated that dynorphin (DYN) and the kappa opioid receptor (KOR) system contribute to various psychiatric disorders, including anxiety, depression, and addiction. More recently, this endogenous opioid system has received increased attention as a potential therapeutic target for treating alcohol use disorders. In this review, we provide an overview and synthesis of preclinical studies examining the influence of alcohol (ethanol [EtOH]) exposure on DYN/KOR expression and function, as well as studies examining the effects of DYN/KOR manipulation on EtOH's rewarding and aversive properties. We then describe work that has characterized effects of KOR activation and blockade on EtOH self-administration and EtOH dependence/withdrawal-related behaviors. Finally, we address how the DYN/KOR system may contribute to stress-EtOH interactions. Despite an apparent role for the DYN/KOR system in motivational effects of EtOH, support comes from relatively few studies. Nevertheless, review of this literature reveals several common themes: (i) rodent strains genetically predisposed to consume more EtOH generally appear to have reduced DYN/KOR tone in brain reward circuitry; (ii) acute and chronic EtOH exposure typically up-regulate the DYN/KOR system; (iii) KOR antagonists reduce behavioral indices of negative affect associated with stress and chronic EtOH exposure/withdrawal; and (iv) KOR antagonists are effective in reducing EtOH consumption, but are often more efficacious under conditions that engender high levels of consumption, such as dependence or stress exposure. These results support the contention that the DYN/KOR system plays a significant role in contributing to dependence- and stress-induced elevation in EtOH consumption. Overall, more comprehensive analyses (on both behavioral and mechanistic levels) are needed to provide additional insight into how the DYN/KOR system is engaged and adapts to influence the motivation effects of EtOH. This information will be critical for the development of new pharmacological agents targeting KORs as promising novel therapeutics for alcohol use disorders and comorbid affective disorders.

Orexin/Hypocretin and Organizing Principles for a Diversity of Wake-Promoting Neurons in the Brain

An enigmatic feature of behavioural state control is the rich diversity of wake-promoting neural systems. This diversity has been rationalized as 'robustness via redundancy', wherein wakefulness control is not critically dependent on one type of neuron or molecule. Studies of the brain orexin/hypocretin system challenge this view by demonstrating that wakefulness control fails upon loss of this neurotransmitter system. Since orexin neurons signal arousal need, and excite other wake-promoting neurons, their actions illuminate nonredundant principles of arousal control. Here, we suggest such principles by reviewing the orexin system from a collective viewpoint of biology, physics and engineering. Orexin peptides excite other arousal-promoting neurons (noradrenaline, histamine, serotonin, acetylcholine neurons), either by activating mixed-cation conductances or by inhibiting potassium conductances. Ohm's law predicts that these opposite conductance changes will produce opposite effects on sensitivity of neuronal excitability to current inputs, thus enabling orexin to differentially control input-output gain of its target networks. Orexin neurons also produce other transmitters, including glutamate. When orexin cells fire, glutamate-mediated downstream excitation displays temporal decay, but orexin-mediated excitation escalates, as if orexin transmission enabled arousal controllers to compute a time integral of arousal need. Since the anatomical and functional architecture of the orexin system contains negative feedback loops (e.g. orexin ➔ histamine ➔ noradrenaline/serotonin-orexin), such computations may stabilize wakefulness via integral feedback, a basic engineering strategy for set point control in uncertain environments. Such dynamic behavioural control requires several distinct wake-promoting modules, which perform nonredundant transformations of arousal signals and are connected in feedback loops.

Kappa Opioids, Salvinorin A and Major Depressive Disorder

Opioids are traditionally associated with pain, analgesia and drug abuse. It is now clear, however, that the opioids are central players in mood. The implications for mood disorders, particularly clinical depression, suggest a paradigm shift from the monoamine neurotransmitters to the opioids either alone or in interaction with monoamine neurons. We have a special interest in dynorphin, the last of the major endogenous opioids to be isolated and identified. Dynorphin is derived from the Greek word for power, dynamis, which hints at the expectation that the neuropeptide held for its discoverers. Yet, dynorphin and its opioid receptor subtype, kappa, has always taken a backseat to the endogenous b-endorphin and the exogenous morphine that both bind the mu opioid receptor subtype. That may be changing as the dynorphin/ kappa system has been shown to have different, often opposite, neurophysiological and behavioral influences. This includes major depressive disorder (MDD). Here, we have undertaken a review of dynorphin/ kappa neurobiology as related to behaviors, especially MDD. Highlights include the unique features of dynorphin and kappa receptors and the special relation of a plant-based agonist of the kappa receptor salvinorin A. In addition to acting as a kappa opioid agonist, we conclude that salvinorin A has a complex pharmacologic profile, with potential additional mechanisms of action. Its unique neurophysiological effects make Salvinorina A an ideal candidate for MDD treatment research.

Dynorphin-Dependent Reduction of Excitability and Attenuation of Inhibitory Afferents of NPS Neurons in the Pericoerulear Region of Mice

The Neuropeptide S system, consisting of the 20-amino acid peptide neuropeptide S (NPS) and its G-protein coupled receptor (NPSR), modulates arousal, wakefulness, anxiety, and fear-extinction in mice. In addition, recent evidence indicates that the NPS system attenuates stress-dependent impairment of fear extinction, and that NPS-expressing neurons in close proximity to the locus coeruleus region (LC; pericoerulear, periLC) are activated by stress. Furthermore, periLC NPS neurons receive afferents from neurons of the centrolateral nucleus of the amygdala (CeL), of which a substantial population expresses the kappa opioid receptor (KOR) ligand precursor prodynorphin. This study aims to identify the effect of the dynorphinergic system on NPS neurons in the periLC via pre- and postsynaptic mechanisms. Using electrophysiological recordings in mouse brain slices, we provide evidence that NPS neurons in the periLC region are directly inhibited by dynorphin A (DynA) via activation of κ-opioid receptor 1 (KOR1) and a subsequent increase of potassium conductances. Thus, the dynorphinergic system is suited to inactivate NPS neurons in the periLC. In addition to this direct, somatic effect, DynA reduces the efficacy of GABAergic synapses on NPS neurons via KOR1 and KOR2. In conclusion, the present study provides evidence for the interaction of the NPS and the kappa opioid system in the periLC. Therefore, the endogenous opioid dynorphin is suited to inhibit NPS neurons with a subsequent decrease in NPS release in putative target regions leading to a variety of physiological consequences such as increased anxiety or vulnerability to stress exposure.

Molecular Changes in Opioid Addiction: The Role of Adenylyl Cyclase and cAMP/PKA System

For centuries, opiate analgesics have had a considerable presence in the treatment of moderate to severe pain. While effective in providing analgesia, opiates are notorious in exerting many undesirable adverse reactions. The receptor targets and the intracellular effectors of opioids have largely been identified. Furthermore, much of the mechanisms underlying the development of tolerance, dependence, and withdrawal have been delineated. Thus, there is a focus on developing novel compounds or strategies in mitigating or avoiding the development of tolerance, dependence, and withdrawal. This review focuses on the adenylyl cyclase and cyclic adenosine 3,5-monophosphate (cAMP)/protein kinase A (AC/cAMP/PKA) system as the central player in mediating the acute and chronic effects of opioids. This chapter also reviews the neuronal adaptive changes in the locus coeruleus, amygdala, periaqueductal gray, and ventral tegmental area induced by acute and chronic actions of opioid because these neuronal adaptive changes in these regions may underlie the behavioral changes observed in opiate users and abusers.

The role of the dynorphin/κ opioid receptor system in anxiety

Anxiety disorders are the most common and prevalent forms of psychiatric disease, although the biological basis of anxiety is not well understood. The dynorphin/κ opioid receptor system is widely distributed in the central nervous system and has been shown to play a critical role in modulating mood and emotional behaviors. In the present review, we summarize current literature relating to the role played by the dynorphin/κ opioid receptor system in anxiety and κ opioid receptor antagonists as potential therapeutic agents for the treatment of anxiety disorders.

Drug withdrawal conceptualized as a stressor

Drug withdrawal is often conceptualized as an aversive state that motivates drug-seeking and drug-taking behaviors in humans. Stress is more difficult to define, but is also frequently associated with aversive states. Here we describe evidence for the simple theory that drug withdrawal is a stress-like state, on the basis of common effects on behavioral, neurochemical, and molecular endpoints. We also describe data suggesting a more complex relationship between drug withdrawal and stress. As one example, we will highlight evidence that, depending on drug class, components of withdrawal can produce effects that have characteristics consistent with mood elevation. In addition, some stressors can act as positive reinforcers, defined as having the ability to increase the probability of a behavior that produces it. As such, accumulating evidence supports the general principles of opponent process theory, whereby processes that have an affective valence are followed in time by an opponent process that has the opposite valence. Throughout, we identify gaps in knowledge and propose future directions for research. A better understanding of the similarities, differences, and overlaps between drug withdrawal and stress will lead to the development of improved treatments for addiction, as well as for a vast array of neuropsychiatric conditions that are triggered or exacerbated by stress.

Endogenous Opioids: The Downside of Opposing Stress

Our dynamic environment regularly exposes us to potentially life-threatening challenges or stressors. To answer these challenges and maintain homeostasis, the stress response, an innate coordinated engagement of central and peripheral neural systems is initiated. Although essential for survival, the inappropriate initiation of the stress response or its continuation after the stressor is terminated has pathological consequences that have been linked to diverse neuropsychiatric and medical diseases. Substantial individual variability exists in the pathological consequences of stressors. A theme of this Special Issue is that elucidating the basis of individual differences in resilience or its flipside, vulnerability, will greatly advance our ability to prevent and treat stress-related diseases. This can be approached by studying individual differences in "pro-stress" mediators such as corticosteroids or the hypothalamic orchestrator of the stress response, corticotropin-releasing factor. More recently, the recognition of endogenous neuromodulators with "anti-stress" activity that have opposing actions or that restrain stress-response systems suggests additional bases for individual differences in stress pathology. These "anti-stress" neuromodulators offer alternative strategies for manipulating the stress response and its pathological consequences. This review uses the major brain norepinephrine system as a model stress-response system to demonstrate how co-regulation by opposing pro-stress (corticotropin-releasing factor) and anti-stress (enkephalin) neuromodulators must be fine-tuned to produce an adaptive response to stress. The clinical consequences of tipping this fine-tuned balance in the direction of either the pro- or anti-stress systems are emphasized. Finally, that each system provides multiple points at which individual differences could confer stress vulnerability or resilience is discussed.

The kappa opioid receptor: from addiction to depression, and back

Comorbidity is a major issue in psychiatry that notably associates with more severe symptoms, longer illness duration, and higher service utilization. Therefore, identifying key clusters of comorbidity and exploring the underlying pathophysiological mechanisms represent important steps toward improving mental health care. In the present review, we focus on the frequent association between addiction and depression. In particular, we summarize the large body of evidence from preclinical models indicating that the kappa opioid receptor (KOR), a member of the opioid neuromodulatory system, represents a central player in the regulation of both reward and mood processes. Current data suggest that the KOR modulates overlapping neuronal networks linking brainstem monoaminergic nuclei with forebrain limbic structures. Rewarding properties of both drugs of abuse and natural stimuli, as well as the neurobiological effects of stressful experiences, strongly interact at the level of KOR signaling. In addiction models, activity of the KOR is potentiated by stressors and critically controls drug-seeking and relapse. In depression paradigms, KOR signaling is responsive to a variety of stressors, and mediates despair-like responses. Altogether, the KOR represents a prototypical substrate of comorbidity, whereby life experiences converge upon common brain mechanisms to trigger behavioral dysregulation and increased risk for distinct but interacting psychopathologies.

Direct targeting of peptidergic amygdalar neurons by noradrenergic afferents: linking stress-integrative circuitry

Amygdalar norepinephrine (NE) plays a key role in regulating neural responses to emotionally arousing stimuli and is involved in memory consolidation of emotionally charged events. Corticotropin-releasing factor (CRF) and dynorphin (DYN), two neuropeptides that mediate the physiological and behavioral responses to stress, are abundant in the central nucleus of the amygdala (CeA), and directly innervate brainstem noradrenergic locus coeruleus (LC) neurons. Whether the CRF- and DYN-containing amygdalar neurons receive direct noradrenergic innervation has not yet been elucidated. The present study sought to define cellular substrates underlying noradrenergic modulation of CRF- and DYN-containing neurons in the CeA using immunohistochemistry and electron microscopy. Ultrastructural analysis revealed that NE-labeled axon terminals form synapses with CRF- and DYN-containing neurons in the CeA. Semi-quantitative analysis showed that approximately 31 % of NET-labeled axon terminals targeted CeA neurons that co-expressed DYN and CRF. As a major source of CRF innervation to the LC, it is also not known whether CRF-containing CeA neurons are directly targeted by noradrenergic afferents. To test this, retrograde tract tracing using FluoroGold from the LC was combined with immunocytochemical detection of CRF and NET in the CeA. Our results revealed a population of LC-projecting CRF-containing CeA neurons that are directly innervated by NE afferents. Analysis showed that approximately 34 % of NET-labeled axon terminals targeted LC-projecting CeA neurons that contain CRF. Taken together, these results indicate significant interactions between NE, CRF and DYN in this critical limbic region and reveal direct synaptic interactions of NE with amygdalar CRF that influence the LC-NE arousal system.

Locus coeruleus kappa-opioid receptors modulate reinstatement of cocaine place preference through a noradrenergic mechanism

Activation of kappa-opioid receptors (KORs) in monoamine circuits results in dysphoria-like behaviors and stress-induced reinstatement of drug seeking in both conditioned place preference (CPP) and self-administration models. Noradrenergic (NA) receptor systems have also been implicated in similar behaviors. Dynorphinergic projections terminate within the locus coeruleus (LC), a primary source of norepinephrine in the forebrain, suggesting a possible link between the NA and dynorphin/kappa opioid systems, yet the implications of these putative interactions have not been investigated. We isolated the necessity of KORs in the LC in kappa opioid agonist (U50,488)-induced reinstatement of cocaine CPP by blocking KORs in the LC with NorBNI (KOR antagonist). KOR-induced reinstatement was significantly attenuated in mice injected with NorBNI in the LC. To determine the sufficiency of KORs in the LC on U50,488-induced reinstatement of cocaine CPP, we virally re-expressed KORs in the LC of KOR knockout mice. We found that KORs expression in the LC alone was sufficient to partially rescue KOR-induced reinstatement. Next we assessed the role of NA signaling in KOR-induced reinstatement of cocaine CPP in the presence and absence of a α2-agonist (clonidine), β-adrenergic receptor antagonist (propranolol), and β(1)- and β(2)-antagonist (betaxolol and ICI-118,551 HCl). Both the blockade of postsynaptic β(1)-adrenergic receptors and the activation of presynaptic inhibitory adrenergic autoreceptors selectively potentiated the magnitude of KOR-induced reinstatement of cocaine CPP but not cocaine-primed CPP reinstatement. Finally, viral restoration of KORs in the LC together with β-adrenergic receptor blockade did not potentiate KOR-induced reinstatement to cocaine CPP, suggesting that adrenergic receptor interactions occur at KOR-expressing regions external to the LC. These results identify a previously unknown interaction between KORs and NA systems and suggest a NA regulation of KOR-dependent reinstatement of cocaine CPP.

Social stress engages opioid regulation of locus coeruleus norepinephrine neurons and induces a state of cellular and physical opiate dependence

Stress is implicated in diverse psychiatric disorders including substance abuse. The locus coeruleus-norepinephrine (LC-NE) system is a major stress response system that is also a point of intersection between stress neuromediators and endogenous opioids and so may be a site at which stress can influence drug-taking behaviors. As social stress is a common stressor for humans, this study characterized the enduring impact of repeated social stress on LC neuronal activity. Rats were exposed to five daily consecutive sessions of social stress using the resident-intruder model or control manipulation. LC discharge rate recorded 2 days after the last manipulation was decreased in stressed rats compared with controls. By 10 days after the last manipulation, LC rates were comparable between groups. Systemic administration of the opiate antagonist, naloxone, robustly increased LC discharge rate in a manner suggestive of opiate withdrawal, selectively in stressed rats when administered 2 or 10 days after the last manipulation. This was accompanied by behavioral signs of mild opiate withdrawal. Western blot and electron microscopic studies indicated that repeated social stress decreased corticotropin-releasing factor type 1 receptor and increased μ-opioid receptor levels in the LC. Together, the results suggest that repeated social stress engages endogenous opioid modulation of LC activity and induces signs of cellular and physical opiate dependence that endure after the stress. These cellular effects may predispose individuals with a history of repeated social stress to substance abuse behaviors.

Regulated norepinephrine transporter interaction with the neurokinin-1 receptor establishes transporter subcellular localization

Neurokinin-1 receptor (NK1R) mediates down-regulation of human norepinephrine (NE) transporter (hNET) via protein kinase C (PKC). However, native NET regulation by NK1R and the mechanism by which NK1R targets NET among other potential effectors are unknown. Effect of NK1R activation on native NET regulation and NET/NK1R interaction were studied using rat brain synaptosomes expressing native NET and NK1R as well as human placental trophoblast (HTR) cells coexpressing WT-hNET or NK1R/PKC-resistant hNET-T258A,S259A double mutant (NET-DM) and hNK1R. The selective NK1R agonist, GR73632, and Substance-P (SP) inhibited NE transport and reduced plasma membrane expression of NET and NK1R. Pretreatment with the NK1R antagonist, EMEND (aprepitant) prevented these NK1R-mediated effects. Immunoprecipitation experiments showed that NET forms stable complexes with NK1R. In HTR cells, combined biotinylation and immunoprecipitation studies revealed plasma membrane localization of NET·NK1R complexes. Receptor activation resulted in the internalization of NET·NK1R complexes. Lipid raft and immunoprecipitation analyses revealed the presence of NET·NK1R complexes exclusively in non-raft membrane fractions under basal/unstimulated conditions. However, NK1R activation led to translocation of NET·NK1R complexes to raft-rich membrane fractions. Importantly, PKCα was found in association with raft-localized NET following SP treatment. Similar to WT-NET, PKC-resistant NET-DM was found in association with NK1R exclusively in non-raft fractions. However, SP treatment failed to translocate NET-DM·NK1R complexes from non-raft fractions to raft fractions. Collectively, these results suggest that NK1R forms physical complexes with NET and that the receptor-mediated Thr(258) + Ser(259) motif-dependent translocation of NET·NK1R complexes into raft-rich microdomains facilitates NET/NK1R interaction with PKCα to coordinate spatially restricted NET regulation.

Cannabinoid and opioid interactions: implications for opiate dependence and withdrawal

Withdrawal from opiates, such as heroin or oral narcotics, is characterized by a host of aversive physical and emotional symptoms. High rates of relapse and limited treatment success rates for opiate addiction have prompted a search for new approaches. For many opiate addicts, achieving abstinence may be further complicated by poly-drug use and co-morbid mental disorders. Research over the past decade has shed light on the influence of endocannabinoids (ECs) on the opioid system. Evidence from both animal and clinical studies point toward an interaction between these two systems, and suggest that targeting the EC system may provide novel interventions for managing opiate dependence and withdrawal. This review will summarize the literature surrounding the molecular effects of cannabinoids and opioids on the locus coeruleus-norepinephrine system, a key circuit implicated in the negative sequelae of opiate addiction. A consideration of the trends and effects of marijuana use in those seeking treatment to abstain from opiates in the clinical setting will also be presented. In summary, the present review details how cannabinoid-opioid interactions may inform novel interventions in the management of opiate dependence and withdrawal.

κ-Opioid receptors in the central amygdala regulate ethanol actions at presynaptic GABAergic sites

Human and animal studies indicate that κ-opioid receptors (KORs) are involved in ethanol drinking and dependence (Xuei et al., 2006; Walker and Koob, 2008; Walker et al., 2011). Using in vitro single-cell recording techniques in mouse brain slices, we examined the physiologic effects of KOR activation in the central amygdala (CeA) on GABAergic neurotransmission and its interaction with acute ethanol. A selective KOR agonist (U69593, 1 μM) diminished evoked GABAergic inhibitory postsynaptic currents (IPSCs) by 18% (n = 10), whereas blockade of KORs with a selective antagonist (nor-binaltorphimine, 1 μM) augmented the baseline evoked GABAergic IPSCs by 14% (P < 0.01; n = 34), suggesting that the KOR system contributes to tonic inhibition of GABAergic neurotransmission in the CeA. In addition, the enhancement by acute ethanol of GABAergic IPSC amplitudes was further augmented by pharmacologic blockade of KORs, from 14% (n = 36) to 27% (n = 26; P < 0.01), or by genetic deletion of KORs, from 14% in wild-type mice (n = 19) to 34% in KOR knockout mice (n = 13; P < 0.01). Subsequent experiments using tetrodotoxin to block activity-dependent neurotransmission suggest that KORs regulate GABA release at presynaptic sites. Our data support the idea that KORs modulate GABAergic synaptic responses and ethanol effects as one of multiple opioid system-dependent actions of ethanol in the CeA, possibly in a circuit-specific manner.

Development of κ opioid receptor antagonists

κ opioid receptors (KORs) belong to the G-protein-coupled class of receptors (GPCRs). They are activated by the endogenous opioid peptide dynorphin (DYN) and expressed at particularly high levels within brain areas implicated in modulation of motivation, emotion, and cognitive function. Chronic activation of KORs in animal models has maladaptive effects including increases in behaviors that reflect depression, the propensity to engage in drug-seeking behavior, and drug craving. The fact that KOR activation has such a profound influence on behaviors often triggered by stress has led to interest in selective KOR antagonists as potential therapeutic agents. This Perspective provides a description of preclinical research conducted in the development of several different classes of selective KOR antagonists, a summary of the clinical studies conducted thus far, and recommendations for the type of work needed in the future to determine if these agents would be useful as pharmacotherapies for neuropsychiatric illness.

Neuropeptide regulation of the locus coeruleus and opiate-induced plasticity of stress responses

Stress has been implicated as a risk factor in vulnerability to the initiation and maintenance of opiate abuse and is thought to play an important role in relapse in subjects with a history of abuse. Conversely, chronic opiate use and withdrawal are stressors and can potentially predispose individuals to stress-related psychiatric disorders. Because the interaction of opiates with stress response systems has potentially widespread clinical consequences, it is important to delineate how specific substrates of the stress response and endogenous opioid systems interact and the specific points at which stress circuits and endogenous opioid systems intersect. The purpose of this review is to present and discuss the results of studies that have unveiled the complex circuitry by which stress-related neuropeptides and endogenous opioids coregulate activity of the locus coeruleus (LC)-norepinephrine (NE) system and how chronic morphine, or stress, disturbs this regulation.

Overexpression of corticotropin-releasing factor in Barrington's nucleus neurons by adeno-associated viral transduction: effects on bladder function and behavior

The stress-related neuropeptide, corticotropin-releasing factor (CRF), is prominent in neurons of the pontine micturition center, Barrington's nucleus. These neurons co-innervate spinal preganglionic neurons that control the bladder, and locus coeruleus (LC) neurons that provide norepinephrine innervation throughout the brain. Adeno-associated viral (AAV) vector-mediated transfer of CRF cDNA was used to increase CRF expression in Barrington's nucleus neurons and investigate the impact of a gain of function in Barrington's nucleus spinal and LC projections. AAV transfer of the reverse CRF cDNA sequence served as the control. Bladder urodynamics and behavior were assessed 4 weeks after vector injection into Barrington's nucleus. Rats with bilateral injections of AAV-CRF cDNA into Barrington's nucleus had immunohistochemical evidence of CRF overexpression in neurons and transport to the spinal cord and LC. The bladder : body weight ratio was greater and micturition pressure was less in these rats compared with controls, consistent with an inhibitory influence on bladder function. Other indices of urodynamic function were not altered. CRF innervation of the LC was increased in rats with bilateral Barrington's nucleus injections of AAV-CRF cDNA, and this was associated with increased burying behavior, an endpoint of LC activation by CRF. The results provide immunohistochemical evidence for viral vector-induced CRF overexpression in Barrington's nucleus neurons and underscore the ability of AAV vector-mediated transfer to increase CRF function in selective circuits. The findings support an inhibitory influence of CRF in Barrington's nucleus regulation of the bladder and an excitatory influence on the brain norepinephrine system that translates to behavioral activation.

Cannabinoid-1 receptors in the mouse ventral pallidum are targeted to axonal profiles expressing functionally opposed opioid peptides and contacting N-acylphosphatidylethanolamine-hydrolyzing phospholipase D terminals

The ventral pallidum (VP) is a major recipient of inhibitory projections from nucleus accumbens (Acb) neurons that differentially express the reward (enkephalin) and aversion (dynorphin)-associated opioid peptides. The cannabinoid-1 receptor (CB1R) is present in Acb neurons expressing each of these peptides, but its location in the VP is not known. To address this question, we used electron microscopic dual immunolabeling of the CB1R and either dynorphin 1-8 (Dyn) or Met(5)-enkephalin (ME) in the VP of C57BL/6J mice, a species in which CB1R gene deletion produces a reward deficit. We also used similar methods to determine the relationship between the CB1R and N-acylphosphatidylethanolamine (NAPE)-hydrolyzing phospholipase D (NAPE-PLD), an anandamide-synthesizing enzyme located presynaptically in other limbic brain regions. CB1R-immunogold was principally localized to cytoplasmic endomembranes and synaptic or extrasynaptic plasma membranes of axonal profiles, but was also affiliated with postsynaptic membrane specializations in dendrites. The axonal profiles included many single CB1R-labeled axon terminals as well as terminals containing CB1R-immunogold and either Dyn or ME immunoreactivity. Dually labeled terminals comprised 26% of all Dyn- and 17% of all ME-labeled axon terminals. Both single- and dual-labeled terminals formed mainly inhibitory-type synapses, but almost 16% of these terminals formed excitatory synapses. Approximately 60% of the CB1R-labeled axonal profiles opposed or converged with axon terminals containing NAPE-PLD immunoreactivity. We conclude that CB1Rs in the mouse VP have subcellular distributions consistent with on demand activation by endocannabinoids that can regulate the release of functionally opposed opioid peptides and also modulate inhibitory and excitatory transmission.

Stress-induced epigenetic regulation of κ-opioid receptor gene involves transcription factor c-Myc

Exposure to stress is associated with adverse emotional and behavioral responses. Whereas the κ-opioid receptor (KOR) system is known to mediate some of the effects, it is unclear whether and how stress affects epigenetic regulation of this gene. Because the KOR gene can use two promoters (Pr1 and Pr2) and two polyadenylation signals (PA1 and PA2), it is also interesting whether and how these distinct regulatory mechanisms are differentially modulated by stress. The current study examined the effects of stress on these different regulatory mechanisms of the KOR gene. Results showed that stress selectively increased the expression of KOR mRNA isoforms controlled by Pr1 and terminated at PA1 in specific brain areas including the medial-prefrontal cortex, hippocampus, brainstem, and sensorimotor cortex, but not in the amygdala or hypothalamus. These effects correlated with altered epigenetic state of KOR Pr1 chromatin, as well as elevation and increased recruitment of the principal transcription factor c-Myc, which could activate Pr1. Stress-induced modulation of Pr1 was further validated using glutamate-sensitive murine hippocampal cell line, HT22. The results revealed a common molecular mechanism underlying the effect of stress on selected chromatin regions of this gene at the cellular level and in the context of whole animal and identified a critical role for c-Myc in stress-triggered epigenetic regulation of the KOR gene locus. This study sheds light on the mechanisms of stress-induced epigenetic regulation that targets specific chromatin segments and suggests certain KOR transcripts and its principal transcription factor c-Myc as potential targets for brain-area-specific intervention.

The dynorphin/κ-opioid receptor system and its role in psychiatric disorders

The dynorphin/κ-opioid receptor system has been implicated in the pathogenesis and pathophysiology of several psychiatric disorders. In the present review, we present evidence indicating a key role for this system in modulating neurotransmission in brain circuits that subserve mood, motivation, and cognitive function. We overview the pharmacology, signaling, post-translational, post-transcriptional, transcriptional, epigenetic and cis regulation of the dynorphin/κ-opioid receptor system, and critically review functional neuroanatomical, neurochemical, and pharmacological evidence, suggesting that alterations in this system may contribute to affective disorders, drug addiction, and schizophrenia. We also overview the dynorphin/κ-opioid receptor system in the genetics of psychiatric disorders and discuss implications of the reviewed material for therapeutics development.

Predator stress engages corticotropin-releasing factor and opioid systems to alter the operating mode of locus coeruleus norepinephrine neurons

The norepinephrine nucleus, locus coeruleus (LC), has been implicated in cognitive aspects of the stress response, in part through its regulation by the stress-related neuropeptide, corticotropin-releasing factor (CRF). LC neurons discharge in tonic and phasic modes that differentially modulate attention and behavior. Here, the effects of exposure to an ethologically relevant stressor, predator odor, on spontaneous (tonic) and auditory-evoked (phasic) LC discharge were characterized in unanesthetized rats. Similar to the effects of CRF, stressor presentation increased tonic LC discharge and decreased phasic auditory-evoked discharge, thereby decreasing the signal-to-noise ratio of the sensory response. This stress-induced shift in LC discharge toward a high tonic mode was prevented by a CRF antagonist. Moreover, CRF antagonism during stress unmasked a large decrease in tonic discharge rate that was opioid mediated because it was prevented by pretreatment with the opiate antagonist, naloxone. Elimination of both CRF and opioid influences with an antagonist combination rendered LC activity unaffected by the stressor. These results demonstrate that both CRF and opioid afferents are engaged during stress to fine-tune LC activity. The predominant CRF influence shifts the operational mode of LC activity toward a high tonic state that is thought to facilitate behavioral flexibility and may be adaptive in coping with the stressor. Simultaneously, stress engages an opposing opioid influence that restrains the CRF influence and may facilitate recovery toward pre-stress levels of activity. Changes in the balance of CRF:opioid regulation of the LC could have consequences for stress vulnerability.